Nonaqueous electrolyte batteries which use lithium as the negative electrode active material have lately attracted attention as high energy density batteries, and much active research is being conducted.
As a solvent of the nonaqueous electrolyte for these types of batteries, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, sulfolane, dimethoxy ethane, tetrahydrofuran and dioxolane and the like can be used alone or in the form of a mixture of two or more of these substances. As a solute dissolved in the solvent there can be mentioned LiPF.sub.6, LiBF.sub.4, LiClO.sub.4, LiCF.sub.3 SO.sub.3, LiAsF.sub.6, LiN(CF.sub.3 SO.sub.2).sub.2, LiCF.sub.3 (CF.sub.2).sub.3 SO.sub.3 and the like.
Among the nonaqueous electrolyte batteries, one in which a manganese oxide is used as a positive electrode material is attractive because of the possibility of reduction of cost of the positive electrode. As a manganese oxide used as a positive electrode material, there can be mentioned MnO.sub.2, LiMn.sub.2 O.sub.4, LiMnO.sub.2 and the like. A cobalt oxide is also a conventional active material of a positive electrode. As a typical cobalt oxide used as the positive electrode, LiCoO.sub.2 can be mentioned.
However, a battery which uses a manganese oxide or a cobalt oxide as a positive electrode material causes a problem that manganese or cobalt: is eluted into an electrolyte from the positive electrode material, i.e., the manganese oxide or the cobalt oxide, respectively, during charge-discharge cycle or storage, and battery properties, especially storage property, are deteriorated.
It has been proposed to add an aliphatic carboxylic acid or a chain aliphatic carboxylate to an electrolyte to improve the storage property (Japanese Patent Laid-Open Publication No. Hei 5-182689). It has also been proposed to add cerium or yttrium to cobalt oxide of the material of the positive electrode (Japanese Patent Laid-Open Publication No. Hei 5-6779 or Hei 5-6780, respectively).
However, these proposals have still not been satisfactory to solve a problem of self-discharge of a battery. This is because an additive to the electrolyte or additive to the positive material cannot inhibit elution of manganese or cobalt from the positive electrode.